Rapid cytometric assays for lymphocyte activation have many potential clinical applications, including evaluation of cellular immune dysfunction in HIV infection and cancer, assessment of the severity of autoimmune disease processes, tissue typing, and monitoring of transplant recipients for early signs of graft rejection. With a view toward development of reproducible, standardized methods which can be implemented on the current generation of clinical flow cytometers, multiparameter flow cytometry will be used to analyze and correlate changes in RNA content, activation antigen expression, and membrane tracking dye fluorescence in human peripheral T-lymphocytes during the first 24 hours following activation by polyclonal mitogens, alloantigen, or mismatched cells, in a trial of the efficacy of these cytometric indicators of cell activation in comparison with tritiated thymidine incorporation. It is likely that these studies will validate an assay based on detection of RNA content increases using pyronin Y and/or expression of the CD98 activation antigen. PROPOSED COMMERCIAL APPLICATION: Rapid tests for lymphocyte activation have a wide potential range of application in diagnosis and monitoring of immune system disorders.